1. The Field of the Invention
The present invention relates to field emission devices. More particularly, the present invention relates to a field emission device having a gate electrode including a layer of nanocrystalline or microcrystalline silicon that provides improved adhesion with an underlying silicon dioxide layer. The invention is also directed to methods of making and using the field emission device.
2. The Relevant Technology
Integrated circuits and related structures are currently manufactured by an elaborate process in which semiconductor devices, insulating films, and patterned conducting films are sequentially constructed in a predetermined arrangement on a semiconductor substrate. In the context of this document, the term "semiconductor substrate" is defined to mean any construction comprising semiconductive material, including but not limited to bulk semiconductive material such as a semiconductive wafer, either alone or in assemblies comprising other materials thereon, and semiconductive material layers, either alone or in assemblies comprising other materials. The term "substrate" refers to any supporting structure including but not limited to the semiconductor substrates described above. The term semiconductor substrate is contemplated to include such structures as silicon-on-insulator and silicon-on-sapphire.
Computer monitors, televisions, and other visual display devices have traditionally used cathode ray tubes which use an electron gun to direct a scanning electron beam upon a phospholuminescent screen. With the advent of portable personal computers, telecommunication devices, and other such appliances, there has been an increased interest in high quality lightweight display panels that are not as bulky as cathode ray tubes. A promising and useful development has been the incorporation of field emission devices into integrated circuits, semiconductor structures or related products to produce flat panel displays.
A field emission device typically includes an electron emission structure or tip configured for emitting a flux of electrons upon application of an electric field thereto. The emitted electrons may be directed to a transparent panel having phospholuminescent material placed thereon. By selecting and controlling the operation of an array of miniaturized field emission devices, a selected visual display that is suitable for use in computer and other visual and graphical applications may be produced. Flat panel displays using field emission devices typically have a greatly reduced thickness compared to cathode ray tubes. As a result, field emission devices have been shown to be an attractive alternative to cathode ray tube display devices.
Field emission devices used in flat panel displays are generally multilayer structures formed over a semiconductor, glass, or other substrate. FIG. 1 illustrates an example of a field emission device in an intermediate step during the manufacturing process. Multilayer structure 10 comprises two structures that will be used as electrodes during operation of the completed field emission device. In particular, cathode structure 12 and low potential gate electrode structure 14 will be used to establish an electric field across electron emission structure 16. The two electrodes are separated by a dielectric layer 18.
In order to freely emit a flow of electrons, electron emission structure 16 must be exposed during manufacturing by removing material positioned thereon. One of the steps of exposing electron emission structure 16 may include conducting a planarization operation on multilayer structure 10, including a layer 21, by chemical-mechanical planarization or other mechanical or non-mechanical means, thereby producing a substantially planar surface indicated by the dashed line at 20. Layer 21 comprises a conductive material such as chromium, aluminum, alloys thereof, and/or silicon.
When chemical-mechanical planarization is used to expose electron emission structure 16, there is the risk of delamination of layer 21 from dielectric layer 18 if the bonding forces therebetween are not sufficiently strong. Typically, it has been understood that the bonding forces between a silicon dioxide substrate and an overlying silicon layer are related to the internal compressive stress of the overlying silicon layer. Generally, higher compressive stress values tend to correlate with poor bonding and increased risk of delamination. While not a fixed rule, it has been observed in the past that compressive stress less than 2.times.10.sup.9 dynes/cm.sup.2 are preferred in some circumstances in order to reduce the tendency of the layers to delaminate.
Nonetheless, an amorphous silicon layer deposited on a silicon dioxide layer using plasma-enhanced chemical vapor deposition (PECVD) frequently delaminates during a subsequent chemical-mechanical planarization operation, even though the compressive stress of the amorphous silicon layer may be relatively low. The difficulties involved in forming an adequate bond between an amorphous silicon layer deposited using PECVD and a silicon dioxide substrate have generally discouraged the use of PECVD amorphous silicon layers when chemical-mechanical planarization steps are to be conducted thereon. As a result, when chemical-mechanical planarization has been used in the prior art, layer 21 has generally consisted of materials other than amorphous silicon.
However, in general, amorphous silicon is understood to be a preferred material in forming other portions of field emission devices and other semiconductor structures. Moreover, PECVD is a preferred and efficient method for depositing silicon layers over a substrate. The inability to use PECVD amorphous silicon layers as described above when chemical-mechanical planarization operations are subsequently conducted has been a persistent problem that, if overcome, would significantly improve the cost-effectiveness and reliability of the process of manufacturing field emission devices.
In view of the foregoing, it is clear that there is a need for methods of manufacturing field emission devices in which a silicon layer may be deposited by PECVD on a dielectric layer without delaminating during subsequent chemical-mechanical planarization. In particular, it would be an advancement in the art to provide a method for depositing silicon on silicon dioxide to produce a bond sufficiently strong tot resist subsequent delamination in the fabrication of a field emission device.